1. Field of the Invention
This invention relates to an electrically heatable caulking method and, more particularly, to an electrically heatable caulking method adapted for caulking a work made of magnesium or any suitable magnesium alloy and having one or more caulking pins.
2. Description of the Related Art
For instance, a light weight aluminum alloy or a steel plate has been conventionally and widely used as structural members of a vehicle, such as a cylinder head cover or a buffer plate. When these members are secured to another member, a so-called electrically heatable caulking method is widely used as mentioned below. First, caulking pins provided on one of the members are inserted into corresponding caulking pin holes formed in the other member. These two members are thus superimposed together and placed between two opposing electrodes, by which an alternative electric current is supplied between these two members and, in addition, a pressure force is also exerted therebetween.
Also, recently, research has been conducted so as to discover a method using a magnesium or a magnesium alloy, having a specific gravity smaller than that of the above-mentioned aluminum alloy, in place of the latter.
In an application of structural members of a vehicle, it is possible to use a magnesium alloy as the material of a cylinder head cover. However, in the prior art, it has been conventionally considered that, apart from a light weight aluminum alloy, it is technically difficult to use a magnesium alloy in an electrically heatable caulking method for attaching a cylinder head cover made of a magnesium alloy to a buffer plate, because a plastic working of magnesium alloy is more difficult than that of an aluminum alloy and, therefore, according to a conventional caulking method, it is difficult to work the magnesium alloy to a desired shape.